Inhibitors to transfer of structural material constituents in liquid sodium



June 28, 1960 J. w. MAUSTELLER 2,943,034

INHIBITORS T0 TRANSFER OF STRUCTURAL MATERIAL CONSTITUENTS IN LIQUID SODIUM Filed 001;. 19, 1955 SAMPLING GATE VALVE SODI UM LEVEL SODIUM RESERVOIR RA DIO ACTIVE SOURCE HOT LEG (WRAPPED WITH HEATING WIRE) coLb LEG MAGNESIA DRAIN VALVE.

001.0 TRAP i INVENTOR.

* Jol-m/ HI. M40: TELLER flown, M rm -P\-22,943,034 ,nvruBrroRsKTo TRANSFER- on STRUCTURAL CONSTITUENTS} 1N; LIQUID soDI John W. Mausteller, Evans City, Pa, assignor to Mine safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania p 7 FiledOct.19,1955,Ser.lN'4: 541,511-

' 8 Claims. 01. 204-154;

This invention 'relatesjto inhibitors which will decrease the mass transfer of structural material constituents in liqquid sodium and in particular it relates to inhibitors which will decrease the mass transfer of those radioactive species. having a longer half life than'sodium-24, found in structural materials such as stainless steel, mild'steel,

Inconel and similar alloys used to transport liquid sodium in a nuclear reactor.

.JLiquid sodium is used as a heat transfer medium in nuclear reactors; The sodium is circulated through stainless steel pipe or other alloy pipe containing various constituents such as manganese, cobalt, iron, antimony a'nd tantalum which may, become radioactive. These constituentsztend to dissolve in the liquid sodium. and are circulatedthroughout the cooling system of the nuclear reactor. These constituents thereafter deposit on the pip 2' of the reduction of oxygen content, surface plating and salting out by the inhibiton-I' Thus, the inhibited species need :not the, radioactive tobe inhibited; Y 1

Since theradioactive constituents of-structural materials such as stainless steel, Inconel, mild :steel and similar alloys having a half lifez'greater than .sodium-24are iof partlcula'r interest insofar as the inhibition of their transfer in liquid sodium is concerned, the half lives of the more important isotopes as compared to sodium-.24 are presented in the. table below:

Half life isotope: 7 i

Sodium-24 i 15 hours Tantalum-182 117 days Iron-59 i 46 days Manganese-54 310 days Cobalt-60 5.2 years Antimony-124 -a 60 days 7 It is readily apparent from this tablethat the radiation hazard of the isotopes listed can last for several months. It is therefore extremely important to prevent these isotopes from being transported in a liquid sodium system ing outside/thei reactor and present a radiation hazard.

the mass transfer of radioactive constituents found in stainless steel, 'Inconel'and s'imilaralloys. in order. to hold them ass transfer' ofthese constituents toa minimum, it is necessary in liquid sodium systems of this type tornaintain the oxygen contentof the sodium below0'.0l""wt. percent and preferably below"0. 005 wt. percent. However, the relatively small difference in oxygen concentration of0.003' and 0.01 wt. percentwill produce'anincrease in transfer of 3 to 54 fold depending upon the isotope transferred. 'Thus, it has become important to find inhibitors which willdecrease or completely prevent the transfer of these radioactive constituents such as cobalt-60, tantalum-182, manganese-54, iron-59 and antimony-124 in liquid sodium.

One object of this invention is to provide materials which will inhibit the transfer of structural material constit-uents in liquid sodium.

Another object is to provide inhibitors which will decrease or prevent themass transfer of radioactive constituents having a longer half life than sodium-24 which.

are found in structural materials used to transport liquid 7 sodium.

such as barium, strontium, calcium, titanium, antimony.

and magensi-um when used in an amount as little as 1 wt. percent in a liquid sodium heat transfer system using stainless steel or other alloy piping will inhibit the mass transfer of radioactive structural material constituents in liquid sodium. Although the mechanism of inhibition is not completely understood, itlis believed to be a function used to transfer heat from a nuclear reactor especially at temperatures above IZOO F. wheremass transfer has been found to increase at anexponenti al rate.

The attached drawing shows typical apparatus in which the invention may be carried out. p ff;

- The experimental apparatus for testing the effectiveness of various metals as inhibitors'of' isotope transfer in a liquid sodium system consisted of a loop constructed of /2" stainless steel pipe which was large enough to contain 450 g. of sodium. Thebottom of theloop'was equipped 'with a 12"length of /2" stainless steel pipe opening into the loop atits upper end and closed at its lower end and operable as a. cold trap for-oxide impurities as described in the copending application of Batutis and Walters, Serial- No. 538,447, filed October 4, 1955, now Patent"No.= 2, 879,l 57',' issued March 3, 1959; A drain valve'was' also inserted in the bottom of the loop adjacent the cold trap. A 1%" stainless steel pipe connected to the top of the loop'servedas an'expansion tank. This tank' was fittedwith a 1 /2" gatevalve for sampling and access to the radioactive source. -Two rod-type lheaters-were inserted-in the top of "the loop adjacent the expansion tank to-supply heat to 'thesys'tem. One'leg of the loop was insulated and the otherleg was not. The temperature of the liquid sodium was obtained from a thermocouple located in the bot-tom of the expansion tank. Circulation of the liquid sodium was maintained by thermal convection.

The operating procedure used to test various metals as transfer inhibitors in the apparatus described was as follows: the loop was cleaned-with a 8:1:1 mixture of water, nitric acid and hydrochloric acid, rinsed with water and evacuated to dryness. All valves were disassembled, cleaned with naphtha, dried and reassembled.

The loop was then filled with 450 g. of sodium filtered at 350 F. This method of cleaning and filling usually resulted in an original oxygen content of less than 0.005

wt. percent. If the oxygen content was greater than this value, a short period of cold trapping would remedy the situation. The cold, uninsulated leg of the loop was heated with a torch to melt the sodium and 1 wt. percent of inhibitor was added through the gate valve. When the temperature of the liquid sodium reached 1000 -15 F., the radioactive source was inserted through the gate valve. The entire system was operated at this temperature for30 days. At the end of this time, the radioactive source was removed through the gate valve into an argon-filled glass apparatus. The liquid sodium was drained from the system at 1000 F., to prevent precipitation of dissolved materials on the pipe walls. After cooling the loop to room temperature, the cold trap was removed and methanol was added to the loop until all reaction ceased as indicated by hydrogen bubbles. Water was finally flushed through the system to remove residual caustic. Tests of the methanol and Water showed that no significant amounts of radioactive material were removed from the walls. Sections of the stainless steel pipe were cut out, flattened, and tested for radioactivity with a radiation counter. The radiation count of each test specimen was compared with the radiation count of a control treated in the same manner except that no inhibitor was added. All inhibitors were rated on the basis of an inhibitor factor calculated as gross radiation count on the control divided by gross radiation count on the sample. Thus, the higher the factor, the better the inhibitor. A factor lower than 1 indicates acceleration of mass transfer.

Several metals were tested'and rated as inhibitors with From the results obtained, it is obvious that barium was the best inhibitor of all the metals tested followed by strontium, calcium, titanium, antimony and magnesium in that order. All the elements in Group IIA of the periodic table were good inhibitors except beryllium. The most significant feature of the good inhibitors was that they were predominantly those which would reduce sodium oxide and apparently formed a protective film on loop surfaces.

Although 1 wt. percent of inhibitors was used in the experiments described, it should be understood that other concentrations may be used if desired. Analyses of materials transported in several of the tests showed that the inhibition of specific isotopes is dependent upon the inhibitor used. Thus, a combination of two or more of the inhibitors disclosed is also considered to be within the spirit and scope of the present invention.

Having thus described this invention fully and completely as required by the patent laws, what is desired to be claimed and secured by United States patent is:

1. The combination with a heat exchange system adjacent a radio-active source wherein liquid sodium is used as a heat transfer medium to absorb heat near said radie-active source, and from which heat is extracted at a point more remote from said source, of a small amount of a metal dissolved in said liquid sodium, said metal being selected from the group, consisting of barium, strontium, calcium, titanium, antimony and magnesium.

2. A combination according to claim 1 in which the metal used is present in about 1 wt. percent of the sodium used.

3. A combination according to claim 2 in which the metal used is barium.

4. A combination according to claim 2 in which the metal used is strontium.

5. A combination according to claim 2 in which the metal used is calcium.

6. A combination according to claim 2 in which the metal used is titanium.

7. A combination according to claim 2 in which the metal used is magnesium.

8. A method of inhibiting mass transfer of radioactive elements, which have a half-life longer than that of sodium-24, in a circulating stream of molten sodium wherein said molten sodium is first heated and then cooled during circulation, which comprises incorporating in said molten sodium a small amount of a metal, said amount being effective to inhibit mass transfer in said sodium, selected from the group consisting of barium, strontium, calcium, titanium, antimony and magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 1,837,744 Zworykin Dec. 22, 1931 FOREIGN PATENTS 648,293 Great Britain J an. 3. 1951 OTHER REFERENCES Smithells: Metals Reference Book, Interscience Publishers, Inc. (1949), page 335. I

Liquid Metals Handbook, Sodium (NaK) Supplement, sponsored by Atomic Energy Commission and the Bureau of Ships, Dept. of the Navy, 3rd edition, June 1955, pages 13-18, 146. 

1. THE COMBINATION WITH A HEAT EXCHANGE SYSTEM ADJACENT A RADIO-ACTIVE SOURCE WHEREIN LIQUID SODIUM IS USED AS A HEAT TRANSFER MEDIUM TO ABSORB HEAT NEAR SAID RADIO-ACTIVE SOURCE, AND FROM WHICH HEAT IS EXTRACTED AT A POINT MORE REMOTE FROM SAID SOURCE, OF A SMALL AMOUNT OF A METAL DISSOLVED IN SAID LIQUID SODIUM, SAID METAL BEING SELECTED FROM THE GROUP, CONSISTING OF BARIUM, STRONTIUM, CALCIUM, TITANIUM, ANTIMONY AND MAGNESIUM. 